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24 iulie 2014

Simple oscilator for testing cristals

Yesterday I was a little bored and I was staring to a box full of quartz cristals. I was wondering what frequency was, especially a very old one with russian marks on it. I know from an elder that the number on the Russian cristal is not the frequency but some sort of code. Stupid, eh?After I contemplate various possibilities of transistor oscillators, I came up with a simple, reliable and versatile TTL configuration, "a classic" to say it simple.
It's a 74LS00 oscillator in series configuration, the schematics is pretty self explanatory.
Now I cand measure with precision the exact frequency of my 38.9 MHz crystals which, by the way, are overtone! I will make nice filters for 12.95 MHz on long winter days!Without a quartz crystal, it self-oscillate around 50 MHz with a very nice sinus wave!